Machine tools using manual positioning such as milling machines (knee mill, bed mill, gantry mill, horizontal mill), laths and grinders are ubiquitous in the manufacture of workpieces (mechanical components). These machines incorporate manually operated hand wheels or levers producing axial motion controlled by the machinist. Frequently, a machine tool screw to which a hand wheel is fixed converts the rotary motion of the hand wheel to linear motion. The magnitude of this rotary hand motion may be determined by examining the dial associated with each hand wheel. Using such a system the machinist remains in complete control of the cutting and shaping process. The terms "relative tool motion" and "positioning the tool" refer to relative movement between the tool, i.e., the cutter and the workpiece. Such relative tool motion may be obtained by moving the tool in three directions (x,y,z) relative to a fixed workpiece, moving a table having the workpiece fixed thereto in the x and y directions and the tool in the Z direction, or other movements of the tool and/or workpiece. For example, the machinist may move a table in the x and y directions and the motor rotated cutting tool in the z direction, each direction of movement being controlled by a separate hand wheel. The accuracy, precision and speed necessary to machine a component (workpiece) is a reflection of the machinist's skill.
Despite the flexibility and ease of use by such manually controlled machine tools, several limitations exist. The burden of precisely positioning the tool falls on the machinist, who may, with a single lapse in concentration position the tool to an unintended place or beyond a part boundary, irrevocably damaging the component. Furthermore, coordinated multiaxis motion produced by simultaneously turning two hand wheels cannot be reliably or accurately reproduced limiting the manual machining process to movement along a single axis followed by movement along a different axis.
The use of a digital readout (DRO) device in conjunction with this type of manual machine tool is intended to assist the machinist in positioning the tool. A DRO utilizes a position feedback sensor, such as an encoder, linear scale or other position transducer to directly report the current position of the tool with respect to a predefined coordinate frame. The tool's position is shown on a digital display. Some DROs support advanced position displays with features like multiple coordinate systems, "distance to travel" displays and way points. DROs, however, do not prevent unintended positioning errors or excessive travel errors by the machinist, nor do they assist the machinist in performing multiaxis coordinated moves.
A computer numerically controlled (CNC) machine tool utilizes computer controlled motors in addition to the position feedback signals to precisely machine components. They may machine components using simultaneous multiaxis coordinated motion. Once the part program (computer software) is prepared these CNC machines can run unattended. However, compared to manual machine tools, CNC systems are expensive and require considerable training before an operator can program and use them. Thus, CNCs are not always economical, particularly when small batches of simple components are to be machined and it may not be economical for a small machine shop to purchase a CNC.
Accordingly, it is an object of this invention to provide improved methods and systems assisting machinists in positioning a tool on manual controlled machines where it is desirable to move the tool to a target position within a known tolerance.
It is also an object of this invention to provide improved methods and systems for assisting manual machines in moving the tool along a known path within a predetermined tolerance zone during contouring operations, even if the path contains complex coordinated multiaxis motions.
It is a further object of this invention to assist manual machinists with pocketing operations on a workpiece by preventing motion that would violate any of the boundary surface constraints defining the pocket.
It is a further object of this invention to allow for the quick, consistent, precise and accurate machining of mechanical components regardless of a machinist's skill level or experience and without a CNC system.